Object References, Mutability, and Recycling — Chapter 9: Understanding Python’s Memory Model

This blog is part of my Fluent Python series.

Link to Chapter 8

variable is reference to an object.

Introduction

Python’s memory management model is both elegant and sometimes surprising. Understanding how objects are referenced, copied, and recycled is fundamental to writing efficient and bug-free Python code. In this chapter, we’ll explore Python’s memory model by examining variable references, object identity, copying mechanisms, and parameter passing behaviors.

When working with Python, it’s crucial to understand that variables don’t “contain” objects — they reference them. This distinction becomes particularly important when working with mutable objects like lists and dictionaries, where unexpected behavior can occur if you don’t fully understand the reference mechanism.

Variables Are References

In Python, a variable name holds a reference to the actual object, not the object itself. This means that when you assign a variable to another variable, both variables reference the same object.

a = [1, 2, 3]
b = a
a.append(4)
b
# Output: [1, 2, 3, 4]